DINOSAUR SMILES: DO THE TEXTURE AND MORPHOLOGY OF THE PREMAXILLA, MAXILLA, AND DENTARY BONES OF SAUROPSIDS PROVIDE OSTEOLOGICAL CORRELATES FOR INFERRING EXTRA-ORAL STRUCTURES RELIABLY IN DINOSAURS?

Were the teeth of dinosaurs exposed or covered to some degree by extra-oral structures? This question has a significant bearing on dinosaur biology: facial structure, eating habits, and social behaviors of dinosaurs must have been influenced by these features. While previous studies have examined jaw and cranial muscles and nerves in extant sauropsids and applied these findings to dinosaurs, few have examined the anterior regions of the sauropsid jaw. It is often noted that the texture, size, and number of extra-oral foramina are correlated with the presence or absence of extra-oral tissues. Here, I seek to test the hypothesis that there is a significant, quantitative correlation between the number of extra-oral foramina on the cranialforward bones and overlying soft tissues among extant sauropsids. Utlizing an Extant Phylogenetic Bracket (EPB) approach, I further hypothesize that morphometrically similar trends between extant sauropsids and dinosaurs should be most parsimoniously consistent with the presence or absence of extra-oral coverings in dinosaurs. Soft tissue dissection, linear measurements, and morphometric analysis of three cranialforward jaw bones (premaxilla, maxilla, dentary) in extant saruopsid specimens (turtles, lizards, snakes, crocodilians, birds) as well as certain mammalian taxa were recorded over a large and varied sample size. Additionally, the premaxillae, maxillae, and dentary bones in the several dinosaur taxa were compared to the extant sauropsid sample to constrain inferences regarding the presence of their extra-oral tissues. Preliminary morphometric data analyses show that the number of extra-oral foramina is statistically correlated with the presence or absence of extra-oral tissues. According to linear analysis, those organisms whose habitat is generally aquatic have more extra-oral foramina. Contrastingly, those animals with dry, terrestrial environments have few or no foramina per each jaw bone studied. Interestingly, dinosaurs fall within the range of snakes, a group known for its extra-oral coverings of the teeth. The preliminary results of this study support my hypothesis that foramina number is correlated to some degree with extra-oral structures, possibly indicating innervation and blood supply. This relationship should be pursued in future research.